Screen printing machine with adjustable bridge

ABSTRACT

A SCREEN PRINTING MACHINE HAS A PLURALITY OF CYLINDRICAL THIN-WALLED SCREEN STENCILS THE ENDS OF WHICH ARE SUPPORTED IN STENCIL HOLDERS MOUNTED ON A BRIDGE EXTENDING ACROSS THE FRAME HALVES OF THE MACHINE WITH THERE BEING A BRIDGE FOR EACH STENCIL. AN INNER SQUEEGE FOR DYE PASTE IS ADJUSTABLE WITH RESPECT TO THE STENCIL AND IS MOUNTED IN SUSPENSION SUPPORTS AT BOTH ENDS OF THE STENCIL. EACH BRIDGE IS PARALLEL TO ITS RESPECTIVE STENCIL AND THE STENCIL HOLDERS AND SUSPENSION SUPPORTS ARE SLIDEABLY AND LOCKINGLY MOUNTED ON THE BRIDGE. AT LEAST ONE DRIVE GEAR IS DRIVINGLY CONNECTED THROUGH A MATING GEAR ON EACH STENCIL WITH THE DRIVE GEARS PROTRUDING THROUGH THE UPPER SURFACE OF A FRAME HALF AND ALL THE DRIVE GEARS BEING DRIVINGLY CONNECTED TO A SINGLE DRIVE SHAFT MOUNTED IN A FRAME HALF AND DRIVEN FROM A SINGLE MOTOR.

Feb. 27, 1973 J. G. VERTEGAAL 3,718,086

SCREEN PRINTING MACHINE WITH ADJUSTABLE BRIDGE Filed June 30, 1970 ll Sheets-Sheet 1 xv/ IE] JACOBUS G. VERTEGAAL 5 NVENTOR ATTORN Feb. 27, 1973 J. G. VERTEGAAL 3,718,086

SCREEN PRINTING MACHINE WITH ADJUSTABLE BRIDGE ll Sheets-Sheet 2 Filed June 30, 1970 Feb. 27, 1973 J. G. VERTEGAAL ,0 6

SCREEN PRINTING MACHINE WITH ADJUSTABLE BRIDGE ll Sheets-Sheet 3 Filed June 30, 1970 Feb. 27, 1973 J. G. VERTEGAAL 3,713,086

SCREEN PRINTING MACHINE WITH ADJUSTABLE BRIDGE Filed June 30, 1970 ll Sheets-Sheet 5 1 r16 l I l,

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' I I I7 I 18 49 I I 3 i n ll l I I 12 58 w R 1 2r l L l, I 'I Feb. 27, 1973 3,718,086

SCREEN PRINTING MACHINE WITH ADJUSTABLE BRIDGE J. G. VERTEGAAL ll Sheets-Sheet 6 Filed June 50, 1970 Feb. 27, 1973 J. G. VERTEGAAL 3,718,086

SCREEN PRINTING MACHINE WITH ADJUSTABLE BRIDGE Filed June 50, 1970 ll Sheets-Sheet 7 55 PRINTING WIDTH 2400 PRINTING WIDTH PRINTING WIDTH I620 PRINTING WIDTH I PRINTING WIDTH l6 Feb. 27, 1973 J. G. VERTEGAAL 3,718,036

SCREEN PRINTING MACHINE WITH ADJUSTABLE BRIDGE ll Sheets-Sheet 8 Filed June 30, 1970 Feb. 27, 1973 J. G. VERTEGAAL 3,718,086

SCREEN PRINTING MACHINE WITH ADJUSTABLE BRIDGE ll Sheets-Sheet 9 Filed June 30, 1970 Feb. 27, 1973 J. G. VERTEGAAL 3,718,086

SCREEN PRINTING MACHINE WITH ADJUSTABLE BRIDGE Filed June 50, 1970 ll Sheets-Sheet l0 a m X mun nu II- I l I: l N K l I I *1 \IV F 5 q a I||L J| Feb. 27, 1973 J. G. VERTEGAAL 3,718,086

SCREEN PRINTING MACHINE WITH ADJUSTABLE BRIDGE Filed June 50, 1970 ll Sheets-Sheet ll United States Patent 9 U.S. Cl. 101115 8 Claims ABSTRACT OF THE DISCLOSURE A screen printing machine has a plurality of cylindrical thin-'walled screen stencils the ends of which are supported in stencil holders mounted on a bridge extending across the frame halves of the machine with there being a bridge for each stencil. An inner squeegee for dye paste is adjustable with respect to the stencil and is mounted in suspension supports at both ends of the stencil. Each bridge is parallel to its respective stencil and the stencil holders and suspension supports are slideably and lockingly mounted on the bridge. At least one drive gear is drivingly connected through a mating gear on each stencil with the drive gears protruding through the upper surface of a frame half and all the drive gears being drivingly connected to a single drive shaft mounted in a frame half and driven from a single motor.

The present invention relates to a screen printing machine comprising a plurality of cylindrical thin-walled screen stencils, more particularly, to the structures for supporting the stencils and squeegees for the dye paste and the mechanism for driving the stencils.

Screen printing machines have been known wherein a plurality of cylindrical thin-walled screen stencils have their ends supported in stencil holders with each stencil holder having a central passage for the squeegee. Each screen stencil has an inner squeegee for the dye paste with this squeegee being adjustable with respect to the stencil. The squeegee is fastened in suspension supports at both ends of the stencil. A disadvantage of such known screen printing machines is that it is not possible to use thin-walled cylindrical screen stencils of different lengths within a particular range of lengths. One reason why stencils of varying lengths cannot be used is that the stationary frame of the screen printing machine comprises two parallel frame halves having a fixed spacing therebetween with the stencil holders being mounted on the frame halves. Another problem occurs since the thinwalled cylindrical screen stencils under certain conditions can only be unilaterally driven. The tensioning of the stencils is an important consideration in the driving thereof. In such machines it has been preferable to drive each stencil from its ends at the stencil holders or in the vicinity thereof. This, in effect, is a double-sided drive.

It is therefore the principal object of the present invention to provide a novel and improved screen printing machine which is able to print with a number of stencils of varying lengths wherein the stencils may have a length arbitrarily shorter than the maximum length.

It is another object of the present invention to provide a screen printing machine wherein the cylindrical thinwalled stencils are simply and effectively driven from one end thereof.

It is a further object of the present invention to provide a screen printing machine the adjustment and operation of which is considerably facilitated and simplified.

According to the present invention a screen printing machine comprises a frame having frame halves with a plurality of bridges mounted across the frame halves.

Stencil holder means each having a central passage therethrough are slideably and lockably mounted on each bridge. A corresponding plurality of cylindrical thinwalled screen stencils have their ends mounted in the stencil holders so that each stencil is parallel to its respective bridge. Suspension support means are slideably and lockably mounted on each bridge on both ends of each stencil. An inner squeege for dye paste is provided for each stencil and is mounted on the suspension support means so as to be adjustable thereon with respect to the stencil. The common lower plane tangential to the stencils on the printing machine is lower than the bridges, the stencil holders and the suspension support means.

It is a feature of the present invention that each frame half is provided with a plurality of drives for the stencils so that a stencil may be driven from either side thereof. However, generally only one drive is used and this occurs when one of the two stencil holders is not positioned at one of the bridge ends. This positioning is used when a stencil is being utilized whose length is shorter than the maximum permissible length of a stencil as defined by the distance between the spaced frame halves.

The stencil holder means may comprise a stationary holder casing which is slideably coupled to the bridge and within which is provided an inside mechanism for drivingly connecting the end of a stencil with a gear drive in a frame half.

In order to prevent torsion or the formation of folds or wrinkles in the thin-walled cylindrical screen stencil when a one-sided drive is used tensioning means are provided for the stencil. Each bridge comprises a tensioning device for the screen stencils with the device being capable of exerting an adjustable force against the stencil holder at the non-driven end of the stencil with this force being in a direction away from the other stencil holder.

In order that no components on the bridge interfere along the width of the web which is to be printed, where a one-sided drive is used one of the stencil holders is slideable on the bridge so that no portion thereof protrudes downwardly beyond the stencils. The driving means for a stencil comprises a drive gear which protrudes upwardly above the top surface of the frame for engagement with an external gear mounted on the end of the stencil. A protective hood is provided which encloses the drive gear when it is not drivingly engaged with a stencil. The hood is so arranged that upon the removal of a stencil from the drive gear the hood automatically closes over the drive gear.

The drive means for the stencils are further provided with an adjusting arrangement whereby the stencils can be rotated with respect to each other in order to provide a fine adjustment even while the external gear on each stencil is already in mesh with its respective drive gear.

Other objects and advantages of the present invention will be apparent upon reference to the accompanying description when taken in conjunction with the following drawings, which are exemplary, wherein:

FIG. 1 is a perspective view of a portion of a screen printing machine incorporating the present invention illustrating the manner in which two stencils of one equal length are mounted thereon;

FIG. 2 is a perspective view of one end of a stencil showing the associated drive arrangement therefor;

FIG. 3 is a perspective view of a bridge showing a stencil holder and stencil tensioning device mounted thereon;

FIGS. 4- and 5 are perspective views of a portion of a bridge showing the stencil holders mounted thereon with FIG. 4 showing the holder in the process of being mounted and FIG. 5 showing the holder in position;

FIG. 6 is a side elevational view of a suspension support with associated suspended squeegee with the squeegee being secured to a squeegee holder;

FIG. 7 is a perspective view of a stencil holder and a portion of a frame half and showing a feeler electrode for indicating the quantity of dye paste in the stencil;

FIG. 8 is a diagram illustrating a number of possible applications of stencils of different printing lengths which may be employed in the screen printing machine according to the present invention;

FIG. 9 is an exploded perspective view showing two different inside mechanisms which can be mounted in a stencil holder;

FIG. 10 is a longitudinal sectional view taken along the line X-X of FIG. 11 of a stencil holder having an inside mechanism according to the present invention;

FIG. 11 is a front elevational view of the stencil holder according to the present invention;

FIG. 12 is a longitudinal sectional view corresponding to that of FIG. 10 but showing a stencil holder having a modified inside mechanism;

FIG. 13 is a side elevational view of a stencil holder having an inside mechanism accordin to FIG. 12; and

FIG. 14 is a perspective view of the driving box in a frame half of the printing machine with a portion of the box being cut away and the cover detached therefrom.

Proceeding next to the drawings wherein like reference symbols indicate the same parts throughout the various views a specific embodiment and modifications of the present invention will be described in detail.

As may be seen in FIG. 1, the screen printing machine according to the present invention comprises stationary frame halves 1 and 2 which are parallel to each other and which determine the maximum length of a stencil 3. Also shown in FIG. 1 is a portion of a stencil 4 having a length shorter than the maximum. A plurality of bridges 5 are mounted across the frame halves 1 and 2 and perpendicular thereto. Each bridge has a protruding portion 6 secured in a bracket 7 mounted upon a frame half 1. The bridges 5 may also be secured to the frame halves in a manner as disclosed in the copending US. patent application S.N. 51,042, now US. Pat..No. 3,675,- 571 by the applicant who is the assi-gnee of the present invention.

The underside of each bridge 5 is spaced at some distance above the fiat upper surface of the frame halves 1 and 2. The arrangement is such that the undersides of the bridges 5 are higher than the lower portions of the stencils 3 and 4 so that these portions of the stencils extend downwardly beyond the lower most portions of the bridges.

Mounted on each bridge 5 are two stencil holders 8 and two gallows-shaped suspension supports 9 for the squeegees. Each stencil holder 8 comprises a casing 10 secured to the bridge 5 and an inside mechanism of which only a rotatable sleeve 11 with an annular flange 48 is visible. Squeegee blades 51 are secured to squeegee holders 12 in a known manner with the holders being hollow and serving simultaneously as a dye feeding tube. For this purpose the squeegee holders 12 are connected to feed pipes 13. In a known manner, a hydraulically or pneumatically operated unit 14 couples the squeegee holder 12 to the suspension support 9. The unit 14 is fed through a pipe 15 and can be vertically adjusted by a knob 16. At one end of a stencil the squeegee holder 12 may be clamped by means of a member 19 in a block 18 mounted at the lower end of a plunger 17 extending from the unit 14. At the other end of the stencil the squeegee holder 12 is inserted in a supporting ring 20 secured to the plunger 17.

The holder casings 10 and the suspension supports 9 for the squeegees are slideably mounted along the bridge 5 with respect to each other so that they can be secured to the bridge at any desired location along its length. Since the casings l0 and the suspension supports 9 can be slid under bridges 5 it is preferable that the projection 6 and bracket 7 should be smaller than the bridges.

The squeegee suspension supports 9 and the holder casings 10 can be freely hung on the bridge 5. For this purpose there is provided a channel-shaped member 21 which is mounted on the upper surface of the bridges 5 with the casings 10 being hung thereon in a manner as shown in FIGS. 4 and 5. The adjustment support 9 can be locked on the channel member or gutter 21 by an adjusting screw 22. The suspension of the casings 10 is preferably in such a manner that they can be tilted upwardly. The stencils with respect to the direction of movement of the web as indicated by the arrow 23 can be lifted as they are mounted on the rear faces of the bridges as shown in FIG. 1.

The channel 21 is also employed for tensioning the screen stencil and for this purpose comprises recesses or slots 24 in which tensioning devices 25 and 26 can be locked. The tensioning device 25 comprises a block while the tensioning device 26 comprises a slide 27 which is capable of being locked in the channel 21 and a rod 29 which by means of a target lever 28 can be drawn out wardly. The rod 29 serves to push the non-driven stencil holder 10 away from the driven stencil holder on the same stencil.

As may be seen in FIG. 1 the stencils 3 and 4 have their ends secured in the holder casings 10 Within inside mechanisms with one casing carrying an external gear 30 and the other casing not having such a gear. That end of a stencil which is not positioned above a stationary frame half but hangs freely on a bridge 5 and over the space between the halves of the frame is provided with an inside mechanism including a rotatable sleeve 11 without an external gear. The rotatable sleeve 11 has an outer dimension which is smaller than the diameter of the stencil and is supported in a stationary ring of the holder casing 10.

Proceeding next to FIG. 2 there is illustrated the right hand portion of the longer stencil 3 which is shown in FIG. 1 mounted on frame half 2. The stencil 3 is driven by a drive gear 31 which is rotatably supported inthe stationary frame half 2 and which protrudes upwardly above the top surface of the frame half through a slot 32. A gear wheel 31 meshes with the external gear 30 mounted on the rotatable sleeve 11 as described above. In FIG. 2, the suspension and the holder for the squeegee and also the feed tube for the dye are omitted for purposes of clarity. Since the web to be printed moves in the direction of the arrow 23 the stencil 3 rotates in the direction indicated by the arrow 33. As a result drive gear 31 rotates in the direction of the arrow 34. A hood 35 shown in the left portion of FIG. 2 covers the slot 32' when there is no stencil holder 8 mounted over a drive gear.

The hood 35 is provided with a rubbing member with brake block 87 (as may be seen in FIG. 14) which cooperates with the drive gear 31 and which retains the hood at all times in its closed position when the hood is not open. When the stencil holder 8 is to be positioned over a slot 32, the hood is moved by hand in the direction of the arrow 36 which is opposite to the direction of rotation of the drive gear under the hood. The hood is provided with a nose 37 which functions as a handle with this nose being shown in broken lines in the opened pm sition and at 37 in the closed position in FIG. 2. The hood may also be secured by a structure as disclosed in the copending US. patent application Ser. No. 51,042, now U.S. Pat. No. 3,675,571 whose applicant is the same as the assignee of the present application.

As may be best seen in FIG. 3, the bridge 5 is freely supported in bracket 7 which are mounted on both sides of the machine on the frame halves 1 and 2. In FIGS. 1, 2 and 3, tensioning means are shown to increase the rigidity of the bridge by means of a tension rod 38 within the hollow bridge 5. The ends 39 of the bridge are constructed as end covers and carry nuts 40 mounted on the ends of tension rod 38 to prestress the bridge. The rod 38 insures that the stencil tensioning devices 25 and 26 do not bend the bridge which would result if a non-uniform load were applied to the stencil. This positioning of the tension rod 38 is also disclosed in the copending U.S. patent application Ser. No. 51,042, now US. Pat. No. 3,675,571 where the applicant is the same as the assignee of the present invention and is asymmetric.

As may also be seen in FIG. 3, a graduated scale 42 is provided around the end of the rotatable sleeve 11 which end is visible from the front face 41 of the holder casing 10. The scale 42 is positioned on this front face 41. With these scale graduations and by means of a rotatable disk 43 mounted on a frame half 2., the respective stencils which are positioned in series on the screen printing machine can be brought into registration with respect to each other in such a manner that the patterns on the screen printing stencils correctly overlap each other. This adjustment is a fine adjustment since when the screen stencils are mounted the mutual angular displacement of the patterns on the stencils with respect to the mutual spacing of the stencils as viewed in the direction of move ment 23 has already been taken into account. Thus, the scale graduations 42 on each stencil provide a coarse registration of the stencils.

The mounting of the stencil holders 8 on the bridge is shown in FIGS. 4 and 5. A surface of the holder casing is provided with a strip 44 which fits into the channel member 21. The holder casing 10 is provided with a U- shaped recess which fits around the bridge 5 and the blocks 45 rest against abutments 46 on the bridge. The stencil holder 8 is shown in FIG. 5 in its operative position on the bridge 5. It is apparent from FIG. 5 that the stencil holder 8 is slideably mounted on the bridge and that the stencil holder is capable of tilting. During operation, a stencil holder can be lifted by tilting upwardly in a direction opposite to the direction of the arrow 47.

The holder casing 10 has an opening 72 (see FIG. 9) but which is not shown from FIGS. 4 and 5. In FIGS. 4 and 5 the inside mechanism together with the rotatable sleeve 11 is already mounted in the holder casing 10. The inner surface of the sleeve 11 is cylindrical and the inside mechanism is hollow in order to accommodate the squeegee structure and the dye feeding tube. In FIGS. 4 and 5 one can see an annular flange 48 of the sleeve 11 of the inside mechanism in which an end ring 65 of the stencil is mounted by means of a bayonet joint as may be seen in FIGS. 10 and 12. Another form of coupling for the rotatable sleeve 11 to the end ring of the stencil is disclosed in applicants copending Netherlands patent application Ser. No. 6910510.

The suspension support 9 for the squeegee is shown in FIG. 6 and comprises a pair of legs 49 by which the support can be mounted on the bridge 5 in a manner similar to that of the holder casing 10. A locking bolt 22 is provided on a leg 49. The squeegee holder 12 is on the side of the stencil mounted in a block 18 with a clamping member 19. The unit 14 enables a squeegee blade 51 to be vertically adjustable with respect to the stencil 3 and the web 52 which is to be printed. The unit 14 urges the block 18 downwardly by means of plunger 17 over a predetermined distance while an eccentric 53 is provided which is adjustable by means of a wheel 16 with which the height of the squeegee can be adjusted.

The gallows-shaped suspension support 9 is provided with a vertical slit 54 having a reverse or elbow-shaped slit 55 at its upper end. As may be seen from FIG. 2, the suspension support 9 has a channel cross section. The slit 54 is on both sides of the support and these slits slideably receive pins 56 mounted on a rod 57 which is pivotally connected by pin 58 with the block 18. The length of the rod 57 can be adjusted by means of a screw thread 59 which is on an extension 69 of the rod 57. When the sliding pins 56 are hung in the reverse slit 55,

6 the squeegee blade 51 is in its inoperative position and cannot possible damage the stencil during the process of the operations required for inserting and mounting thereof.

As shown in FIG. 7, a feeder electrode 61 for checking the quantity of dye paste is inserted in the stencil 3 by mounting the electrode in a holder 62 secured to the support 3 and adjustable in height by means of a nut 63 in order to regulate the dye level in the stencil. An electric lead 64 can be curved around to the stationary frame in the manner as shown in the drawing. In FIG. 8 there is shown a diagram of a number of different possible printing widths for the screen printing machine according to the present invention. The ends of the stencils are provide with the fixed rings 65 which are received within the rotatable sleeves 11 upon which are mounted the external gears 30. The stencil holder casings are indicated at 10. Resilient members 66 are provided for determining the longitudinal stress in the stencil after the stencil has been tensioned. The resilient member 66 also function to provide a certain amount of self-adjusting action for the bearing of the rotatable sleeve of the inside mechanism on the non-driven side of the printing machine. As indicated in the diagram, a stencil is driven on that one side on which the external gear 30 is provided. As is apparent in the diagram, the resilient member 66 is mounted on the side of the stencil opposite to the side on which the gear 30 is provided. Thus, the end of the stencil having the resilient member 66 is the non-driven end. It is apparent from the diagram of FIG. 8 that the stencil holder should have two types of inside mechanisms, namely, an inside mechanism with a spring but without an external gear and an inside mechanism without the spring but with the external gear. These two types of inside mechanisms are illustrated in FIG. 9.

As described above the inside mechanism comprises the rotatable sleeve 11 which may or may not carry the external gear 30 and a stationary ring 67 which fits into the holder casing 10 and is locked therein. The stationary ring 67 is provided with projecting earns 68 which fit in corresponding parts 69 of the casing 10. The parts 68 and 69 are coupled by bolts 70 which are tightened from the front face 41 of the casing 10. In this manner, the stationary ring 67 is locked within the stencil holder 10. The resilient member 66 may or may not be mounted. The rotatable sleeve 11 may carry a fastening collar 71 for the external gear 30. The sleeve 11 also carries the annular flange 48 for coupling with the end ring of the stencil. The pitch circle of the external gear 30 has a diameter which is equal to the diameter of the stencil which is being used.

The drive gear 31 on the stationary machine frame engages the external gear 30 which freely rotates in the holder casing It) through the recess 72 in the underside of the casing as may be seen in FIG. 9. The inside mechanism A as shown in FIG. 9 has an external gear 30 but is not provided with resilient member 66. The inside mechanism B of FIG. 9 does not have the external gear 30 but is provided with the resilient member 66. It is thus possible to construct the inside mechanisms A and B from identical components on the condition that the collar 71 has a diameter smaller than that of the stencil.

In FIG. 10, there is illustrated the inside mechanism B mounted within the holder casing 10. The collar 71, however, is omitted. The rotatable sleeve 11 of the inside mechanism is coupled to the stencil end ring 6-5 by a bayonet joint connection comprising the annular collars 48 and 73 of the sleeve 11 and end ring 65 respectively. The stencils are thus easily interchangeable to the rotatable sleeves 11.

The sleeve 11 is rotatably supported in a stationary ring 67 by means of a bearing 74. The stationary ring 67 is coupled by bolts 75 and a screw spring 76 to the holder casing 10 and with bolts 70 at the cams 69 fitting into the bolts 75.

In FIGS. 12. and 13 there is illustrated the inside work A mounted in the holder casing 10. The coupling be tween the stationary ring 67 is achieved directly by the bolt 70 without interposing a resilient member. It is pointed out that the pitch circle of the external gear 30 is larger than the outer diameter of the coupling 48, 73 but as large as the diameter of the edge 77 of the stencil end ring 65.

The external gear 30 is accessible trough the recess 72 in the underside of the holder casing 10 as shown in FIG. 13. Scale graduations are engraved on the area 42 in the front face 41 of the holder casing 10 as may be seen in FIGS. 11 and 12. A base mark is provided on the annular face 78 so as to be visible from the front face 41. In this manner, the angular displacement of the stencil with respect to its holder casing 10 is indicated at all times. During manufacture, the pattern of the stencil is positioned correctly with respect to the base mark. Obviously, one must take into account the location of each stencil on the screen printing machine or the squeegee and mutual spacing of the stencils.

In FIG. 14 a driving shaft 79, 80 is journaled in frame half 2 only a portion of which is shown. The driving shaft 79, 80 drives all of the drive gears 31 which mesh with the external gears 30 of the inside mechanisms of the stencil holder as described above. The driving shaft is preferably constructed of a plurality of components '79, 80 which are interconnected by couplings 81 and the shaft is driven by a single motor. The driving shaft is mounted in only one of the two frame halves and is essentially at right angles to the stencils. At the level of the drive gear 31 a worm 82 is slideably and nonrotatably mounted by means of a key on the shaft part 80. The Worm is provided with a projecting sleeve 83 which is journaled in a sliding member 84 in such a manner that the sleeve 83 is rotatable but non-slideable. The worm '82 meshes with a worm gear 85 mounted on a single integral shaft 86 which extends across the frame halves and upon which are mounted the two drive gears 31. In FIG. 14, only one end of the shaft 86 is shown. With this drive arrangement it is apparent that rotation of the driving shaft 84} will rotate the drive gears 31.

The sliding member 84 is mounted in such a way that it is axially slideable with respect to the driving shaft 80 but cannot be turned or brought into an inclined position. The sliding piece 84 is provided with a guide roller d which is received in a spiral cam groove 89 formed on the bottom portion of the rotatable disk 43 mounted on a closing plate 88 of the oil-filled driving box of the frame half 2. Rotation of the disk 43 will cause the guide roller 90 to move back and forth in the spiral cam groove 89" so as to axially displace the sliding member 84 with respect to the driving shaft 80.

The sliding member 84 supports the sleeve 83 of the worm 82 rotatably but non-slideably. The worm 82 is slideably but non-rotatably mounted on the shaft 80 so that a rotation of the disk 43 produces a displacement of the worm 82 on the shaft 80. This displacement of Worm 82 rotates worm gear 85' and subsequently the drive gear 31. This mechanism thus enables each disk 43 associated with a stencil to be rotated individually so that the stencils which are non-rotatably coupled to the drive gears 31 can still be individually adjusted with respect to each other in the direction of rotation. The disk 43 thus provides a fine adjustment of the registration of the individual stencils.

It is therefore apparent that the screen printing machine according to the present invention embodies several novel features which are advantageous in the operation of such a machine. The stencil holders and the suspension supports for the squeegee are slideably and lockably mounted on the bridges so that these components can be selectively positioned across the width of the Web which is being printed. These slideable components do not project below the stencil and thus there is no possibility of these components penetrating through the web to be printed as it passes beneath the stencils.

The stencils mounted across the frame halves of the machine may be driven by means of driving gears located on both sides of the frame. Thus, stencils having a length less than the maximum length may be arranged at either end of the corresponding bridge and can be unilaterally driven by means of the driving gear provided at that end of the bridge.

The stencil holder according to the present invention comprises a stationary casing and an inside mechanism which is advantageous since the stencil holder can be easily removed from the bridge and the stencil can be easily disengaged from its stencil holders. With this arrangement it is possible to change over quickly to a stencil of another length. The inside mechanism can also be rernoved as a unit and be replaced which, as disclosed above, was necessary when changing over from a maximum to non-maximum stencil length, or on changing from a stencil driven on one side of the machine with a non-maximum length to a similar stencil which is driven from the other side of the machine.

With the one-sided stencil drive according to the present invention for each stencil the rotatable sleeve of one inside mechanism has an external gear with a pitch circle having a diameter corresponding with that of the stencil whereas the outer dimensions of the rotatable sleeve of the other inside mechanism in which there is no external gear is smaller than the pitch circle. This relationship prevents the rotating sleeve of the latter inside mechanism from protruding through the web being printed. An external gear as large as the circumference of the stencil has advantages on transmission of power and on applying a load to the stencil.

The rigidity of the bridge ensures the required axially directed tensioning force from the stencil. This tension ing on one point of the stencil holder is possible because of the rigid bridge along which the stencil holders may slide.

The friction or braking block provided on the hoods covering the drive gears has the further advantage that the inevitable clearance in the several components of the drive is always absorbed in the same manner so as to facilitate a correct registration of successive stencils.

The tiltable mounting of the stencil holders has the further advantage in that if by accident an object is on the Web to be printed this object will not damage the stencil but will merely lift the stencil as the object passes under the bridge and contacts the stencil.

The squeegee within each stencil is readily retracted from the interior thereof by providing for the squeegee supports to be suspended from the supporting bracket in an inoperative position wherein the squeegee is lifted from contact with the stencil.

A fine adjustment is provided whereby each stencil may be turned with respect to the other stencils while the stencils are drivingly engaged with the drive gears on a frame half. This rotation. of the individual stencils brings the patterns on the stencils in, registration with respect to each other so that no misprinting of the Web occurs. Even though all of the drive gears for the several stencils are driven from a single drive shaft drivingly connected to a single motor a rotatable disk is provided on a frame half by means of which individual stencils can be rotated to obtain registration of the patterns thereon.

It is understood that this invention is susceptible to modification in order to adapt it to diiferent usages and conditions and, accordingly, it is desired to comprehend such modifications within the invention as may fall within the scope of the appended claims.

What is claimed is:

1. In a screen printing machine, the combination of a frame having frame halves, a plurality of bridges mounted across said frame halves, stencil holder means each having a stencil passage therethrough, at least one of said bridges has one pair of said stencil holder means slidably and lockably mounted thereon, a cylindrical thinwalled screen stencil having its ends mounted in such pair of said stencil holder means and lying parallel to its respective bridge, suspension means outside both ends of each stencil for supporting an inner squeegee within the stencil, said suspension means being slidably and lockably mounted on each bridge, said suspension means permitting an adjustment of the squeegee with respect to said stencil, the common lower plane tangential to said stencils being lower than said bridges, the stencil holder means and the suspension means, each stencil holder means comprising a casing slidably attached to a bridge, a stationary ring mounted within said casing and detachably connected thereto, a rotatable sleeve within said stationary ring, bearing means between said stationary ring and said rotatable sleeve, an end ring for a screen stencil detachably connected to said rotatable sleeve, an external gear on the rotatable sleeve of one out of each pair of stencil holder means, said gear having a pitch circle with a diameter corresponding to that of the stencil, and further comprising resilient means on each bridge acting against the other of each pair of stencil holder means in a direction away from the first mentioned stencil holder means for tensioning the screen stencil supported thcrebetwcen.

2. In a screen printing machine as claimed in claim 1 and comprising a drive gear in each frame half and protruding through the upper surface thereof and drivingly engageable to an external gear of a stencil holder means, a pivotally mounted protective hood positioned over said drive gear and pivotable to a position to expose said drive gear, a friction block mounted on said hood and engageable with a face of said drive gear, said hood pivoting to its closed position over the drive gear when the holder casing of a stencil is removed from the drive gear.

3. A screen printing machine as claimed in claim 2 wherein the external gear is detachably secured on said rotatable sleeve, the stationary ring mounted within said casing of each stencil holder means comprising means for coupling said ring to said casing, there being an opening in the underside of said casing through which said external gear of the one stencil holder means meshes with one of the drive gears, and a bayonet joint on said rotatable sleeve and on said end ring for interconnecting said stencil to said drive gear.

4. In a screen printing machine as claimed in claim 11 and comprising means on said bridge for hooking said stencil holder means and suspension means thereon.

5. In a screen printing machine as claimed in claim 1' wherein at least one of said suspension means comprises an upright bracket having a vertical portion and a horizontal arm extending from the upper end thereof, there being a vertical slit in said vertical portion with a reverse slit at its upper end, a squeegee holder mounted from said bracket and having said squeegee thereon, a pin pivotally mounted on said squeegee holder and slideably received within said vertical slit, said squeegee being retained in its inoperative position when said pin is within said reverse slit.

6. In a screen printing machine as claimed in claim 4 wherein said hooking means consists of a U-shaped channel member with upright standing legs, such member being mounted on the upper surface of each bridge, said suspension means and said stencil holder means each having first and second surfaces at right angles to each other, a suspension strip on the first surfaces of both of said suspension means fitting between said legs of said channel member, the respective second surfaces engaging a vertical surface of the bridge, said bridge vertical surface being on the rear face of said bridge with respect to the direction of movement'of the web, there being spaced slots in said channel member, means slideably mounted on said channel member and cooperating with said stencil holder means for tensioning a screen stencil on the bridge, and key means on said stencil tensioning means for lockingly positioning said stencil tensioning means along said channel member.

7. In a screen printing machine as claimed in claim 1 and comprising an adjustable pre-tensioned rod mounted within the side of the bridge away from the respective stencil so as to minimize a bending at the bridge due to the tensioning of the stencil.

'8. In a screen printing machine as claimed in claim 2 wherein there are a plurality of pairs of said drive gears corresponding to the plurality of bridges on the machine frame and each pair of drive gears mounted on a gear shaft, one drive gear of each pair being in a frame half, means for driving said drive gears on a single motor and comprising a drive shaft mounted in a frame half at right angles to the gear shaft, a worm gear on each gear shaft, a worm non-rotatabiy and slideably mounted on said drive shaft and each worm drivingly engaging a worm gear, a projecting sleeve portion on said worm, slideable means for rotatabiy but non-slideably supporting each of said projecting sleeves, a guide roller on said slideable supporting means, and a disk rotatably mounted on a frame half and having a spiral cam groove therein receiving said guide roller whereby rotation of said disk slides 'said worm and turns its respective worm gear to obtain an angular adjustment of the drive gear corresponding to said disk.

References Cited UNITED STATES PATENTS 1,739,264 12/1929 Simpson 101115 X 2,928,340 3/1960 Stein et al 101124 X 1,526,266 2/1925 De Smet 101115 2,071,824 2/1937 Engert 101-116 2,084,827 6/1937 Schwartz et al. 101-115 3,304,860 2/1967 Vander Winden 10l128.1 X 3,566,784 3/1971 Mitter 101120 FOREIGN PATENTS 1,169,337 11/1969 Great Britain.

279,529 3/ 1970 Austria. 1,289,487 12/1962 France.

78516 7/ 1955 Netherlands.

ROBERT E. PULFREY, Primary Examiner E. H. EICKHOLT, Assistant Examiner U.S. Cl. X.R. 101-120 

